http://www.whispermountain.net/CaribouCountyInteroperablePlan.pdf
This document seems to be saying that 700 Mhz is best for Caribou County
Caribou County already has a few 700 MHz radios and can communicate with other counties that are on 700 MHz. The counties with smaller rural populations, such as Caribou, will probably take some time to fully become part of the 700 system simply due to funding issues. As I understand it, all Idaho counties have submitted written plans to become part of the system, but how and when these plans get implemented is another question.
Dave